Assassin/Ninja Powdering A Rainbow Weapon

I don't want to make my weapon into a rainbow weapon, but how should i powder a weapon that already has 5 element damage? Such as the dagger Alizarin.

 

i wouldnt worry too much about that, you'll still end up with a similar damage whatever you choose.
you might want to put 2xt6 water (curse) for a mana regen/water dmg based or 2xt6 thunder (chain lightning) for a mana/life steal build.
also, don't waste too much money on powdering alizarin, there are better weapons out there.